2009.5 G8 GT X-Pipe mod (photos)

[Mike P]

Cool exhaust mod! Sweet thread.......



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[Fatdaddy]

how much was it install of the xpipe?

I paid $160 for the stainless Magna flow X-pipe and the 409 stainless straight pipe. Another $50 to have it put in. It can be done for less with aluminized pipe and a little more with 304 stainless pipe.

I wanted the thermal qualities to match as close as possible so I used the exact same pipe as factory. (I pay attention to details like that.)

[Patrick G]

Here are the dyno results. While you can see that I made a solid 6-8rwhp/rwtq gain under the curve, I had some knock retard slip in around 5400 rpm that didn't allow the "after" graph to stay consistently above the "before" dyno run. Without the KR, the peak difference would have shown a 8-10rwhp gain. Peak torque gain was a 10 lb ft increase. The before power/torque was 336/346 and the after power/torque was 342/356. Thanks to Kurt Decker from LSX Performance Power Tuning for use of his dyno tonight. For around $100 in parts, this is a worthwhile mod, especially since it's drone free.

Mitch (Fatdaddy), my graph was an exact overlay of yours in hp and tq until the knock retard at 5400. Our vehicles are extremely similar in mods and power.

[616 of 933]

I am going to say that its a 2.5 inch pipe? i got my answer 2.25

[Torqued]

Thanks for taking the time to dyno this mod. I think a pair of Kooks midlengths are in my future now. Looking forward to more of your tests. Can't wait till you install one your spec'd cams...

[G8V8]

Nice gain for such a small investment. you used 2.5 tubing and Fatdaddy used 2.25. do you think it matters which size is used? Is one size easier to install?

Are there different sizes of MF Tru-X? If so, which did you use?

Care to speculate what you might get from this mod with Kooks 1 7/8 mids and high-flow cats?

Grrrr8 job. Thanks.

[Patrick G]

Nice gain for such a small investment. you used 2.5 tubing and Fatdaddy used 2.25. do you think it matters which size is used? Is one size easier to install?

Are there different sizes of MF Tru-X? If so, which did you use?

Care to speculate what you might get from this mod with Kooks 1 7/8 mids and high-flow cats?

Grrrr8 job. Thanks.

A this power level, I don't think you'll see a gain or loss between 2.25" and 2.5" pipes. I chose 2.5" because I will be making above this power level in the future. Both pipes are equally easy to install. The Magnaflow X comes in a variety of sizes. I used 2.5" x 12" size.

I think the mid-length Kooks would add another 16-20 rwhp whereas the long tubes would add 20+.

[G8V8]

Thank you. i'm going to look for a local shop to do the welding. It looks like the size of the X is a perfect match to the spacing of the stock pipes. It looks really clean.

[johnbell2]

Thanks, Patrick.

I'm still trying to figure out why GM put in the extra cats and that nasty crimp above the tunnel brace what a mess. A drop from 2.25" to 1 7/8" with a transition back to 2.25" is ugly. That's about a 25-30% drop in effective flow rate in that section alone.

I need to find a reputable shop in Austin TX to get this done. Anyone local have any tips?

[G8V8]

I think they reduced the size to get the flow rate high enough in DOD mode so that the resonators would be effective.